As is known, rakes are used in farming for turning over forage after cutting and accumulating the processed material in rows, normally referred to as windrows.
One of the commonly used rakes is the star-wheel type.
A star-wheel rake comprises a plurality of rakes or star wheels, which are idly mounted on a frame about respective parallel axes and, in practice, form rotating rakes. The rake wheels, with the same diameter, are oblique with respect to a direction of travel in the working configuration and are set in rotation by contact with the ground during the forward travel of the rake. Each rake wheel is equipped with an outer ring of coplanar teeth, shaped to collect the forage and move it sideways due to the combine effect of the rake advancing in the direction of travel and the rotation of the rake wheel about the respective axis. Furthermore, the rake wheels are placed side by side so that the forage moved from the more forward wheels with respect to the direction of travel is collected by the more rearward adjacent wheels. In this way, the rake wheels define a working front and move the forage collected on the working front during forward movement towards a discharge side of the rake, where a windrow is formed. The upstream (more forward) wheels along the working front can partially overlap the immediately adjacent more downstream (more rearward) wheels, to avoid losing the material being processed.
Star-wheel rakes have the advantage of a very simple structure, which does not require specially provided drives for the rake wheels. As already mentioned, the rake wheels are actually idle and rotate due the effect of contact of the teeth with the ground during forward movement. Star-wheel rakes are therefore inexpensive and relatively immune to malfunctioning, and this makes their use fairly widespread.
However, the same mechanism that drives the rake wheels, also causes soil and dust to be raised, which mixes with the collected forage and accumulates in the windrows. Dirt in the forage is obviously unwelcome, because it may interfere with the aeration and drying process and, in general, degrades the quality of the product. Thus, on one hand, star-wheel rakes are inexpensive and good value for money, but on the other, the results they provide are often unsatisfactory.